Nitash P. Balsara Lawrence Berkeley National Lab

May 15, 2013

Project ID # ES088

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Polymer Electrolytes For Advanced Lithium Batteries

Overview • Timeline for projects A and B: • Project start date: October 2010 • Project end date: September 2013 • Percent complete: 90%

• Budget: • Total project funding: $1,990K

–DOE share (100%) –Contractor share (0%)

• Funding received in FY12 $590K • Funding for FY13 $590K

• Barriers: (1) Energy density (2) Safety (3) Low cycle life

• Partners: • ANL, ALS (at LBNL) and NCEM

(at LBNL)

Objectives • A) Develop cost-effective method for creating

nanoporous separators. • B) Study the effect of electrolyte nanostructuring on

dendrite formation in symmetric and full cells. Also studied gas diffusion through SEO.

• C) Develop a binder that conducts ions and electrons.

Milestones • A) Quantify the effect of the nature of the pore structure on conductivity in

porous block copolymer separators and Celgard (Dec. 2012).Completed. David Wong joined ITRI (Taiwan) as a post-doc.

• B) Quantify effect of nanostructuring on dendrite resistance in full cells (Dec. 2012). Completed. Dan Hallinan joined Florida State as an Assistant Professor.

• Project transitioned to BES to solve “needle-in-a-haystack” problem. [Joint paper with Dan Hallinan (EERE-supported student) and Katherine Harry (BES-supported student) submitted.]

• C) Quantify diffusion of gases (CO2, O2, H2O) through SEO copolymers to provide insight into failure of solid Li-air cells (Mar. 2013). CO2 and O2 Completed . Humidity controlled experiments turned out to be challenging due to water absorption in SEO.

• D) Improve on loading of cathodes with conducting binder to 70 wt.%. Completed. Anna Javier is still in my group, transitioning to a non-BATT project.

Approach and Deployment

N-SS

O

O

O

O

F

FF

F

FF

Li+

• Synthesize block copolymers • Study morphology and ion and electron transport • Build and test full cells • Work toward commercialization (either by founding start-ups or by working with companies).

CH

H2C

H2C

CH2

OHyxs-Bu

Nanostructured solid electrolyte

Salt, LiTFSI

Electron- and ion-conducting binder

Nanoporous separator

Add PS homopolymer and then wash it out with THF.

sacrificial polymer

separator polymer

polyethylene separator

mol. wt. of sacrificial polymer

Advantages: Simple wet process (potentially using water) and reduced defect density. Barriers addressed: cost and safety.

Celgard®, σ=0.42 mS/cm

Technical Accomplishment (A): Self-assembled separators

Overall Approach (B): Nanostructured block copolymer electrolytes

We use a solid block copolymer electrolyte SEO to prevent the formation of Li dendrites. The high modulus of the PS block resists dendrite formation and enables the use of lithium metal as an anode.

CH

H2C

H2C

CH2

OHyxs-Bu

PS PEO

high modulus high conductivity

Major Finding: Increasing molecular weight improves both mechanical properties and ionic conductivity.

Technical Accomplishment (B): Quantified gas diffusion through SEO electrolytes

M. Minelli, M. Baschetti, D.T. Hallinan, N.P. Balsara, J. Mem. Sci., 2013

Major Finding: Transport laws developed to understand lithium ion transport also apply to gas diffusion. SEO is unsuitable for selective transport of lithium ions while blocking CO2 and N2, i.e. it cannot help the functioning of the Li-air cell (no go).

Technical Accomplishment: (B) Studied Failure of Li|SEO|FePO4 and Li|SEO|Li ells

Cathode material: LiFePO4

Anode: Li metal

Nanostructured block copolymer electrolyte

D.T. Hallinan, S.A. Mullin, G.M. Stone, N.P. Balsara, J. Electrochem. Soc., vol. 160(3) A464-A470, 2013.

Major Finding: Charge passed to dendrite failure in LiFePO4/SEO/Li batteries is a factor of about 2.5 higher than that of symmetric Li/SEO/Li cells.

Technical Accomplishment (B): Solved “needle-in-haystack” dendrite problem

Li-SEO-Li cell

electrolyte

lithium

lithium

Development of X-ray tomography tool funded by BES (Katherine Harry). Cell building infrastructure built by BATT/EERE (Dan Hallinan).

Technical Accomplishment (B): Finding all “needles-in-haystack” de

ndrit

e vo

lum

e in

ele

ctro

lyte

de

ndrit

e vo

lum

e in

ele

ctro

de

dendrite volume in electrolyte (µm3)

50 μm

50 μm

electrolyte

protrusions

subsurface structures rotation

50 μm

SEM does not reveal sub-surface dendritic structures.

Major Finding: During the early stages of dendrite growth, dendrite is mainly in the electrode.

Technical Accomplishment (C): Development of binder that conducts electrons and ions

this phase conducts electronic charges

N-SS

O

O

O

O

F

FF

F

FF

Li+

-

-

+ Major Technical Accomplishment: Measurement of electronic conductivity of binder as a function of potential.

Ni F

oil

Ni F

oil

-

e-

e- SEO

Li Metal

Li+ Li+

Li+

- Li+

-

-

Li+

Li+

-

-

Li+

- - Li+

Li+

-

+ +

Li+ + e- Li

I = 20 µA + -

FItemoles - =

F = 96485 C/mol Faraday’s constant

merphene monomoles thiomoles eSOC

−

=

Li

Li

S

C6H13

n S

C6H13

n-yyTFSI-

S

C6H13

+ ye-S

C6H13

∗ ∗

Following Chen and Richardson

P3HT

PEO

Technical Accomplishment (C): Conceptual cell design for controlled P3HT oxidation

Technical Accomplishment (C): Three-terminal cell design

Measurement of electronic conductivity (σ) of P3HT as a function of oxidation state (rOX) and potential (Eox).

Technical Accomplishment (C): Measurement of conductivity as a function of oxidation

Quantification of factors that control conductivity of binder.

LiFePO4 Li+ + e- + FePO4

automatic over-discharge protection 70 wt% LiFePO4

Technical Accomplishment (C): Hypothesis of redox reactions in a full cell

Future Work: Lithium-Sulfur Speciation Theory (Prendergast)

Proposed Modeling: Use molecular dynamics simulations and electronic structure calculations to predict spectra.

a1/b1 ratio

S8 0 Li2S8 0.31 Li2S7 0.6 Li2S6 0.8 Li2S5 1.1 Li2S4 1.3 Li2S3 1.5 Li2S2 5

Future Work: Lithium-Sulfur Speciation Experiments and Cell Building

Proposed Experiment: (1) Measure X-ray spectra while the Li-S cell is charged and discharged. (2) Use fundamental knowledge to make Li-S cells that cycle.

Li2Sx in SEO data (not in cell) incident

X-rays

scattered X-rays

Solid electrolyte being developed with Dudney and Tenhaeff (ONRL)

First charge of first cell

Collaboration and Coordination with Other Institutions

Collaborators: Vince Battaglia, Venkat Srinivasan, Jordi Cabana, (LBNL, VT Program). Activity: cell building, testing, and modeling David Prendergast, Jinghua Guo, Miquel Salmeron, Alex Hexemer, Alistair MacDowell (LBNL, outside VT Program). Activity: X-ray spectroscopy and tomography. Nancy Dudney and Wyatt Tenhaeff (ONRL). Activity: Solid polymer/ceramic composites.

Technology Transfer: Cofounded Seeo, a battery start-up, in 2007 to commercialize solid-state battery. Company has moved into pilot production in 2011-12. Batteries sent to customers for testing 2013.

Summary Completed a comprehensive program to study the potential role of nanostructured block copolymers in lithium batteries. • (A) Established a low-cost approach for creating nanoporous

separators. • (B) Quantified the efficacy of SEO copolymers as electrolytes for the

prevention of lithium dendrites in symmetric full cells. • (D) An active binder that conducts both ions and electrons has been

developed, characterized and incorporated into cells. SEO/salt mixture and separator work will be completed by September 2013. (Thank you for your support, critical comments, and guidance.) Transitioning toward understanding and developing all-solid Li-S cells (new BATT project funded in 2012).

Technical Back-up Slides

E-chem oxidation